Vertical shaft impact crushers (VSI-crushers) are used in many applications for crushing hard material like rocks, ore etc. U.S. Pat. No. 3,154,259 describes a VSI-crusher comprising a housing and a horizontal rotor located inside the housing. Material that is to be crushed is fed into the rotor via an opening in the top thereof. With the aid of centrifugal force the rotating rotor ejects the material against the wall of the housing. On impact with the wall the material is crushed to a desired size. The housing wall could be provided with anvils or have a bed of retained material against which the accelerated material is crushed.
To increase the amount of material crushed by the crusher two separate material flows could be fed to the crusher. A first material flow is fed to the rotor. The first material flow is accelerated by the rotor and is ejected towards the housing wall. A second material flow is fed outside the rotor, i.e. between the rotor and the housing. This second material flow is hit by the first material flow ejected by the rotor. Thus the first and second material flows are crushed against each other just outside the rotor.
U.S. Pat. No. 2,012,694 to Runyan describes a crusher where a first flow of material is fed to the centre of a rotating rotor. A second flow of material is fed at the wall of a crusher housing via a feeder comprising two spaced cones. At the housing wall the second flow of material is hit by the first flow of material ejected by the rotor.
U.S. Pat. No. 3,429,511 to Budzich describes a crusher where a first flow of material is fed to the centre of a rotating rotor. A second flow of material is fed via a feeding gap extending around the rotor. The second flow of material forms a continuous curtain of flowing material covering the pathway of the first flow of material just outside the rotor. The first flow of material ejected by the rotor thus hits and crushes the second flow of material.
U.S. Pat. No. 4,662,571 to MacDonald describes a crusher were a first flow of material is fed to the centre of a rotating rotor. A second flow of material is fed into the path of the first material flow accelerated by said rotor before said first material impacts against the crusher wall.
The above crushers do not to utilize the energy of the first flow of material in a very efficient way.